1. Field of the Invention
The present invention relates to a vesicle which is formed of a water-soluble and chargeable block copolymer and, more particularly, to a vesicle which has a useful function as a drug delivery system and various materials.
2. Background Art
It is known that a polymer having a precisely controlled primary structure can be spontaneously organized to form a higher order structure. Specific examples thereof include structures such as micells and vesicles. Such a structure formed by self-organization of a polymer can be subjected to various molecular designs and can be a structure having a novel function in addition to original properties of the polymer. It has hitherto been studied to utilize the structure formed of a self-organized polymer in various fields such as drug delivery systems and materials science.
For example, in Japanese Unexamined Patent Publication (Kokai) No. 8-188541, a part of the inventors of the present invention discloses an electrostatically bonded polymer micell as drug carrier comprising a block copolymer containing a non-chargeable segment and a chargeable segment.
Also, Helmut Schlaad et al., Macromolecules volume 36, number 5, p 1417-1420 discloses that a vesicle referred to as a polymersome can be formed using a block copolymer comprising a poly(1,2-butadiene) block and a poly(cesium methacrylate) block, and a block copolymer comprising a polystyrene block and a poly(1-methyl-4-vinylpyridium iodide) block.
Regardless of expectation of excellent availability, it is often required for the structure formed of a polymer material to use an organic solvent such as chloroform upon production. Furthermore, in the production of a self-organized structure formed of polymers, a complicated operation including several steps is sometimes required. Therefore, it is required to create a structure which has availability and also can be produced by a simple operation.